1. Field of the Invention
The present disclosure relates to a varistor device; in particular, to a varistor device having a specific-melting-point metallic pin.
2. Description of Related Art
Varistors are used as control or compensation elements in circuits either to provide optimal operating conditions or to protect against excessive transient voltages. When used as protection devices, they shunt the current created by the excessive voltage away from sensitive components when triggered. The most common type of varistor is the metal-oxide varistor (MOV). Application of sustained over-voltage to a varistor can cause high dissipation, potentially resulting in the varistor catching fire. A series connected thermal fuse is one solution to varistor failure. However, dissipated heat may degrade the varistor and reduce its life expectancy, and a user may have no indication when the surge suppressor has failed. Furthermore, if the melting point of the thermal fuse is greater than a temperature that would cause the varistor to burst into flames, the varistor may burst into flames before the melting thermal fuse breaks in two to cut off the conducted current; or, the flaming of the varistor and the breaking of thermal fuse may occur at the same time.
As a specific example, the metal oxide varistor disclosed in U.S. Pat. No. 7,453,681 utilizes a fuse to cut off the over-voltages. However, in the heat protection structure of the metal oxide varistor that will automatically go to open circuit in conditions of overheating, the fuse has to be electrically connected between the body and one of the terminals through solder joints. Therefore, the heat may not be able to be conducted to the fuse quickly due to the multiple solder joints, and the heat-shrinkable element wrapped securely around the fuse may not be able to be timely subjected to heat. On the other hand, an insulation bracket is needed to increase the thermal conduction, whereby the heat may be able to be conducted to the fuse more quickly. However, the size and the arrangement of the insulation bracket disposed on the varistor are limited by the size of the varistor, and the insulation bracket may increase the size of the device.